1. Field of the Invention
The present invention relates to a fixing apparatus and an image forming apparatus, and particularly to a fixing apparatus and an image forming apparatus including a temperature detection apparatus detecting a temperature of a heating rotating member in a non-contact manner.
2. Description of the Related Art
A contact type temperature detection apparatus and a non-contact type temperature detection apparatus have conventionally been available as a temperature detection apparatus included in a fixing apparatus. In a contact type temperature detection apparatus, a surface of a fixing member is worn by the temperature detection apparatus in particular in a case where a portion to be detected is located on a heating rotating member such as the fixing member, and image noise results. On the other hand, in a non-contact type temperature detection apparatus, image noise caused by contact is not produced, however, it is characterized by temperature detection accuracy poorer than the contact type.
For example, an infrared sensor or a non-contact thermistor is employed as a non-contact type temperature detection apparatus. An infrared sensor detects infrared rays from a portion to be detected and hence it is excellent in responsiveness. In addition, the infrared sensor is excellent in temperature stability against variation in distance at which it is installed. On the other hand, as the number of pages processed in the fixing apparatus increases, a detection surface is contaminated. As the detection surface is contaminated, responsiveness to variation in temperature at the portion to be detected may become poor or a temperature of the portion to be detected cannot accurately be measured, because a temperature is measured based on a quantity of infrared rays received at the contaminated portion.
Various techniques relating to a conventional fixing apparatus including a non-contact type temperature detection apparatus and a contact type temperature detection apparatus are disclosed.
For example, Document 1 (Japanese Laid-Open Patent Publication No. 05-149790) and Document 2 (Japanese Laid-Open Patent Publication No. 2006-047410) disclose a technique for detecting a temperature of a heating rotating member with both of a non-contact type temperature detection apparatus and a contact type temperature detection apparatus while the heating rotating member remains stopped, finding a detection error therebetween, and correcting a temperature detected by the non-contact type temperature detection apparatus during a rotation period of the heating rotating member based on the error.
In addition, as a technique relating to temperature detection in a fixing apparatus, Document 3 (Japanese Laid-Open Patent Publication No. 2006-184071) discloses a technique for employing a thermistor that has conventionally been used as a contact type temperature detection apparatus as a non-contact type temperature detection apparatus, together with a thermopile representing one example of a non-contact type temperature detection apparatus, and correcting a temperature detected by the thermopile with the temperature detected by the thermistor.
According to the inventions disclosed in Document 1 and Document 2, however, relation between a temperature detected by the non-contact type temperature detection apparatus and a temperature detected by the contact type temperature detection apparatus is not necessarily constant during a period in which the heating rotating member remains stopped and during a period in which the heating rotating member is rotating, and such a situation that unignorable difference between the detected temperature and an actual temperature of the heating rotating member is caused is expected. In addition, according to the invention disclosed in Document 3, if the thermopile is contaminated, such a situation that a temperature of the heating rotating member cannot accurately be detected is expected.
In a case where a temperature of the heating rotating member cannot accurately be detected in the fixing apparatus, a control temperature should be set to a slightly high temperature in order to ensure strength of fixation by the heating rotating member, which leads to increase in power consumption in the fixing apparatus.